1. Field of the Disclosure
The present disclosure relates to an organic light emitting display device (OLED) and a method of fabricating the same, and more particularly, to an OLED whose light extraction efficiency is improved and a method of fabricating the same.
2. Discussion of the Related Art
Following a liquid crystal display, an organic light emitting display device (OLED) characterized by thin thickness, high definition and driving at low power has been drawing an increasing amount of attention as a next-generation display. Reflecting such a current trend, research aimed at mass production of OLEDs has been extensively underway.
In particular, in order to enhance a device, new emission materials have been developed, and a multiple-layered structure for facilitating provision of electrons or holes has been researched. In addition, a technique enhancing efficiency of extracting internally generated light to the outside of a device has been developed.
Currently, light that is not outwardly extracted by total internal reflection in the OLED but blocked takes up 70% or more of the total emission amount, and if this light is outwardly extracted, light efficiency of the OLED may be significantly improved.
FIG. 1 is a cross-sectional view of a general OLED, and illustrates a bottom emission type in which light penetrates in a direction of a substrate 110. According to FIG. 1, the OLED has a structure in which an anode layer 120 formed of indium tin oxide (ITO) and/or indium zinc oxide (IZO), an organic emission layer 130 and a cathode layer 140 formed of a metal, are sequentially stacked on the substrate 110.
Light emitted from the organic emission layer 130 exhibits total reflection on a boundary between the anode layer 120 and the substrate 110. Here, in principal, an amount of the first loss of the light takes up 46% or more of the total emission amount. Also, among the remaining 54% of penetrating light, an amount of a second loss of the light that is totally reflected on the boundary between the substrate 110 and air is 34% or more in principal. Therefore, the light extracted outside of the substrate 110 is 20% or less of an emission rate of light emitted from the organic emission layer 130.
The OLED is formed as an ultra-thin film, and emitted light should penetrate the thin film to be outwardly emitted, so that significant light loss may be caused by the total reflection. When these problems are overcome, the OLED may be more efficiently implemented.